1. Field of the Invention
This invention relates to an operating oil introduction type electromagnetic valve which is prevented from a poor operation due to impure operation oil.
2. Description of the Prior Art
In general, an electromagnetic valve includes a coil which is induced an electromagnetic force by a magnetic current, and a plunger which is attracted and moved by the electromagnetic force of the coil, the plunger being slidably contained inside the coil. In recent times, an operating oil introduction type electromagnetic valve appeared in which an operating oil is introduced to the sliding portion of the plunger in order to cool and lubricate the sliding portion, thereby to be able to achieve a high-speed and high-frequency of operation.
In the case such an electromagnetic valve is located, for example, within an oil tank of a hydraulic oil control circuit of a transmission assembly for an automotive vehicle and is used in the state that the electromagnetic valve is dipped in the operating oil, dust and foreign matter which are mixed in the operating oil somewhere in the circulation path of the operating oil are carried in the oil tank together with the operating oil and then introduced to the sliding portion. This often results in poor operation of the plunger. It is therefore necessary to protect the electromagnetic valve from the impure operating oil.
Japanese utility model early laid-open publication No. 60-52510 discloses one such example. Namely, the publication discloses a pressure control device in which a plunger is directly slidably contained inside a cap for containing operating oil.
However, such a conventional device as described above has still the shortcoming in that dust and foreign matter which are mixed in the operating oil flowing into the cap are accumulated in the sliding portion of the plunger to invite a poor operation.